In a large skillet, cook the beef, onion and green pepper over medium heat until meat is no longer pink; drain. Add the rice, tomato sauce, Worcestershire sauce, salt and pepper. Bring to a boil. Reduce heat; cover and simmer for 10-15 minutes.
Stir in cheese; cover and cook 2-3 minutes longer or until cheese is melted. Spoon 1/2 cup into each pita half.